1. Field of the Invention
The present invention relates to novel coated supports with ultra-thin, single-layer or multi-layer coating, in which the coating material is a polyurethane, further to a process for the production of coated supports of this type and to novel polyurethanes as intermediates for these coated supports.
Coated supports find a multiplicity of uses in industrial technology. For example, the frictional properties of materials may be adapted for a desired purpose by modifying the surface. Furthermore, a protective film may be used for the underlying support in order to preserve their particular surface characteristics. Recently however, coated supports have been used in particular as components in structural elements for optical communications technology and as electronic and optoelectronic information storage.
In particular for the electronic and optical applications it is necessary to produce ultra-thin, defect-free, multi-layer coatings, whose layers have a high degree of order and an adjustable coating thickness which is as homogeneous as possible, it being intended that this high degree of order should also be maintained in the range of a high number of coating layers.
The thin coatings produced from the organic polymers here constitute the basis for defect-free systems which are ordered at the molecular level, as required for example for
optical applications (directional radiation with low attenuation, for example optical fibres with nonlinear optical properties), PA1 electrical applications (electrical conductors with high anisotropy, for example unidimensional or twodimensional conductors in the field of molecular electronics), PA1 "host lattices" for the defined incorporation or a specific bonding of functional groups or molecules (for example biomolecules for sensors). PA1 B is the skeleton of an aliphatic, araliphatic or aromatic diisocyanate, PA1 n assumes values from 2 to 150 and
2. Description of the related art
It is already known to produce monomolecular layers from amphiphilic low molecular weight molecules each having a polar and a nonpolar end, such as long chain fatty acids, on the surface of a nonsolvent such as water, in which layers all the polar ends are directed towards the water for example, while the nonpolar ends project into the gas space above. For this purpose small amounts of amphiphilic substances of this type are dissolved in a suitable solvent and, for example, poured on an aqueous surface of adequate size, where, with evaporation of the solvent, they spread to form a monomolecular layer which initially is not cohesive. By displacing a suitable barrier the aqueous surface is diminished and the associated increase in the surface tension is measured as a function of the surface which still remains available (i.e. plotting thrust-surface diagrams, also termed .pi./A isotherms, which are known to those skilled in the art).
A cohesive monomolecular layer which is ordered at the molecular level is thus produced. On reaching this quasisolid state of this monomolecular layer, further displacement of this barrier meets with a clearly measurable resistance, which indicates that this state has been reached. Suitable supports may then be dipped into the water through the monomolecular layer and on dipping in and/or on withdrawal are themselves covered, with a monomolecular layer of the amphiphilic substance, in which the molecular order is retained in the individual coatings.
The operation mentioned may be repeated. This coating technique is known to those skilled in the art as the Langmuir-Blodgett technique.
Coatings of monomeric amphiphilic substances are however chemically, thermally and mechanically unstable, i.e. the molecular order may be lost by chemical and/or physical influences. It has thus been attempted, to absorb amphiphilic materials having a reactive double or multiple bond onto supports and subsequently to crosslink them to form a polymer, for example by means of high energy radiation.
Diacetylenecarboxylic acids and tricosoic acid are examples which have been investigated many times for the polymerization of unsaturated amphiphilic substances. The serious disadvantage of these substances is their high reactivity, as a result of which they may often be obtained in pure form only with difficulty. Defects, such as macroscopic cracks in the coating, often occur by shrinkage in the course of the polymerization after transfer onto the support.
There have also already been attempts to include polymeric substances such as polystyrene and polymethyl methacrylate in the Languir-Blodgett technique. However, polymers are associated with difficulty in ordering the polar and the non-polar structural components, on the one hand due to the statistical disorder in the polymer chain, and on the other hand due to the super lattices of the polymers. It has thus constantly to be investigated whether the degree of amphiphilic behaviour (i.e. the difference in polarity between the polar and the nonpolar groups) is sufficient in order to achieve coatings with high molecular order and high reproducibility. Here, the so-called Y-structure is often sought, in which, in multi-layer coatings, the polar and the nonpolar structural elements are in each case located opposite one another from one layer to another. For particular applications, for example nonlinear optically active coatings, this Y-structure may be a disadvantage; with the polyurethanes described further below coatings of the X or Z type may also be produced under suitable experimental conditions. In Journal of Molecular Electronics 1 (1985), 3-17 the subject matter referred to is set out in detail.